The present invention relates to controllers, and more particularly to an improved battery powered programmable controller having extended battery life for controlling distant switches such as irrigation valve solenoids.
Programmable irrigation valve controllers are well known in the art. Such controllers are used to open and close irrigation valves by providing electric current to solenoids located in close proximity to the valves. Relatively large electric currents are required to activate and deactivate such solenoids. Providing this required electricity is a simple matter if an external power source is readily available, such as a power line. However, in many commercial agricultural and horticultural situations, controllers must be located at remote field locations where it is impossible or impractical to run a power line or otherwise provide an external power source. In some situations, the valves may be in even more remote locations that are themselves hundreds or even thousands of feet from the controller. Thus, insufficient voltage or current at the both the controller and at the valves is a common problem, especially where long distances or multiple valves are involved. Although some battery powered irrigation controllers have been developed they do not properly address these situations.
A significant limitation of existing battery powered irrigation controllers is battery life. Two voltage levels are generally required by such controllers: a law voltage level (which can be supplied by batteries, e.g. 3.5 volts) to operate the programming circuitry, and a higher voltage level (which can be supplied by a second set of batteries, e.g. 9 volts) to provide the necessary electrical impulses to operate the valve solenoids. The batteries on most existing battery powered controllers must be changed every few weeks or months, making them inconvenient to maintain and potentially unreliable to depend on for controlling irrigation cycles. At least one controller has addressed the problem of conserving the low voltage batteries used to operate the computing circuitry. In U.S. Pat. No. 4,423,484 to Hamilton, the microcomputer is turned off between cycles thereby conserving the low voltage batteries. However, the Hamilton controller does not address conservation of the higher voltage batteries used to operate the solenoids.
It is typical for an irrigation controller to use charging capacitors to operate the valve latching solenoids. These are generally large capacitors of 1000 micro farads or more. Most controllers (including Hamilton) maintain these capacitors in a charged condition, ready for immediate discharge to the solenoid upon receipt of a signal from the microprocessor (see e.g. U.S. Pat. No. 4,718,454 to Appleby). In addition, in most controllers these capacitors have an uninterrupted connection back to the high voltage (e.g. 9, 12, 18 or more volts) batteries from which they are charged. Both of these situations reduce the life of the high voltage batteries, and give rise to other potential problems with the controller.
It is known that all charged capacitors leak over time. This places a constant drain on the high voltage batteries to which they are connected. Such leakage significantly increases with temperature increases. Thus, a fully charged capacitor in a controller located in the middle of an unshaded field during the hot summer months can rapidly deplete the high voltage batteries, even when not in use. The larger the capacitor, the larger the leakage current. Also the higher the ambient temperature, the higher the leakage. This leakage is very significant and could be as much as hundreds of microamps. The leakage causes the capacitor to draw on the battery power supply in order to stay fully charged, thereby wasting energy and leading to the frequent need to change batteries without even any solenoid operation. Preventing this leakage would conserve the life of the high voltage batteries.
Battery operated controllers such as Hamilton use the high voltage batteries for operating both the solenoids and the electronics. Since most low power circuits operate from 3 to 5 volts DC, the high voltage batteries must be reduced and regulated, thereby wasting a considerable amount of energy.
In all controllers, the large capacitors are fully discharged in order to operate the valve solenoids. The capacitors are then recharged from the high voltage batteries. At the instant the discharge occurs, current may also be drawn directly from the high voltage batteries themselves, resulting in unnecessary depletion of the high voltage batteries.
Reliable operation of water valve solenoids is essential to ensure that water is regularly delivered to plants. Typical irrigation systems are designed to use 24 volts of alternating current (AC) to activate and control electric solenoids. However, AC powered irrigation systems suffer from several drawbacks. First, AC voltage drops over long runs of wire such that reliable voltage delivery cannot be assured beyond a few thousand feet. Where multiple solenoids are operated by a single controller, long runs of parallel wires in close proximity to each other may result in capacitive coupling: leakage current and floating voltages induced by energized adjacent wires. This effect may cause unwanted valves to turn on, or fail to cause valves to turn off. Other problems with AC systems include potential burn out of solenoids close to the controller because of excessive primary voltage.
Irrigation valve controlling systems also generally suffer from susceptibility to lightning, and power outages. A lightning strike on a valve in the field can couple onto the buried wires and run back to the controller with devastating results. A power outage can interrupt irrigation cycles potentially inducing stress to vegetation.
A conventional solution to the problem of AC voltage drops over long runs of wire is to provide thick, low-gauge solid wire (e.g. 8 gauge solid copper wire) which has a lower resistance factor than the thinner, higher-gauge wire. This solution provides a reliable method of controlling remote solenoids by decreasing voltage drops. However, the high cost of long runs of low-gauge wire becomes prohibitive, especially when several runs are required to operate several remote solenoids simultaneously. In addition, since the wires are carrying AC, the capacitative, coupling problem is still present.
Another proposed solution is to provide direct current (DC) voltage through long runs of copper wire to the solenoids, since DC systems do not suffer from the capacitive coupling problems of AC systems. However, when copper wires carry DC for long periods of time, the galvanic effect of the inductive field created by buried wires carrying the direct current causes the copper in the wires themselves to deteriorate over time, resulting in unreliability and eventually requiring replacement. For this reason, such DC systems are only used in short distance, above ground installations. These systems also suffer from the general problems presented by lightning strikes and power outages.
A third option is to provide a DC power source at the same remote location as the valve itself utilizing on-site batteries, solar power, or an on-site diesel generator. The disadvantage of this approach is the high cost of a self-contained remote system, and the problems of reliability in the event batteries or generator fail, or the weather is overcast for several days.
My 1994 patent (No. 5,347,421) addresses these problems to some extent by providing an AC power saving module in the form of a local circuit for energizing a solenoid. However, the circuits described in the ""421 patent require a constant (albeit very low) current flow while the valve is open. The low AC current requirements of the ""421 circuits allow much longer or thinner wire run; however, since the wires are carrying AC, the capacitative coupling problem is still present.
The present invention overcomes the disadvantages of prior art irrigation control systems by providing a battery powered switch or irrigation valve controller that conserves the life of both the low voltage batteries which operate the controller circuitry as well as the high voltage batteries which operate the external switches or latching valve solenoids. Such external switches may be located great distances from the controller, and can be in the form of latching relays for industrial control applications such as turning on and off fans, lights, pumps, motors, air conditioners, and the like. The present invention also includes a reliable DC circuit for operating latching solenoids or other remote switches at distances of up to several miles from the battery operated controller. The circuit allows the use of ordinary gauge buried copper wire without concern for possible deterioration of the wires from the galvanic effect of the inductive field created by the buried wires carrying the direct current. The circuits of the present invention also provide an effective deterrent to lightning-induced damage, significantly reduce the current required by the switch or solenoid, and are compatible for use with battery operated control systems. The circuits are simple, inexpensive to build, and energy efficient.
In the battery operated controller of the present invention, two sets of batteries are used. A first set of one or more low voltage batteries (typically 3.0 to 3.6 volts) is dedicated to the operation of the internal circuitry of the controller (e.g. the microprocessor). This low voltage powers the controller circuitry directly without the need for regulation which would otherwise waste energy. In addition, the circuitry is used in a sampling mode such that it is asleep for about 90% of the time. Approximately ten times per second it wakes up and samples the programming inputs for about 10 milliseconds, and then goes back to sleep. The sleep mode power is about 15 microamps while the awake mode draws about 30 microamps, so the average power draw is only about 17 microamps, or a 99% power saving. Occasionally, there will be times when an optional display will be activated, such as during programming changes, which will draw more current (in the range of 2-3 milliamps for a few minutes). This arrangement extends the life of the low voltage battery source for as long as 8 to 10 years.
A second set of one or more high voltage batteries is provided which is only used for charging the capacitors which operate the remote switches or solenoids. This obviates any need to reduce or regulate this battery source for use by the electronic circuitry, so this potential energy loss is avoided.
In the present invention, the large capacitors may be located in close proximity to the switch or solenoid to be energized, which may be a long distance from the controller itself. These capacitors are not charged until just a few seconds before the switch or solenoid is to be energized. At that point, the circuitry enables a transistor or other switching device to turn on and charge such a capacitor through a current limiting resistor. Depending on the voltage of the high voltage batteries, after an appropriate time interval (of between 2 and 20 seconds), for all intents and purposes, the capacitor becomes fully charged. Higher voltage batteries (e.g. 24 or 36 volts) will require a shorter time interval (e.g. 2 seconds) to charge the capacitor; lower voltage batteries (e.g. 9 or 18 volts) will require a longer time interval (e.g. 5 to 10 seconds). Following an isolation step (discussed below), a switching device (e.g. relay, triac, or the like) is used to quickly discharge the capacitor into the remote switch or latching solenoid. Thereafter, the capacitor remains discharged waiting for the next operation. Leaving the capacitor uncharged for long periods of time effectively eliminates capacitive leakage current.
The present invention avoids another source of energy waste found in typical battery operation. With existing controllers, when the capacitor discharges, the charging resistor is still connected from the high voltage battery source to the switch or solenoid. This results in a further draw of current from the battery directly by the solenoid, which also depletes the battery. In the present design, the charging circuit is disabled and isolated by the charging transistor or switch a few milliseconds prior to the capacitive discharge, thereby eliminating this unnecessary power drain. The circuit remains isolated until an appropriate time interval (e.g. a few seconds) before the next operation, at which point the high voltage battery source is again connected to the capacitor for charging followed again by isolation immediately before discharge.
Lithium batteries are recommended for both the low and high voltage circuits. Lithium batteries have extremely long shelf life (10 years), extremely low self discharge (less than 1% per year), and are rated for full performance over a wide temperature range up to 85 degrees Centigrade. Most other types of batteries would self discharge under typical ambient conditions within a year. Also, lithium batteries have double the energy capacity of alkaline batteries, and are lighter in weight.
The circuit board of the present invention and the remote charging circuit may be separately potted (encapsulated) so as to prevent impurities from corroding any of the component parts.
In one embodiment of the invention, the circuitry includes at least one pair of DC power lines which originate from the controller. A single controller can operate several pairs of such power lines, each pair eventually leading through the circuitry described herein to a switch or solenoid in the field. In the field, the incoming pair of power lines is first attached to a relay which controls a set of contacts. When DC power is applied, the relay causes the contacts to close such that power is supplied through a resistor to a capacitor or other DC charge storage device included in the circuit. After a given time interval, depending upon the voltage level provided from the power source, the capacitor becomes substantially fully charged. The power is then shut off at the source which causes the relay to release the contacts which return to their original positions. This causes a secondary circuit to be completed which includes the capacitor and a switch or latching DC solenoid. The completion of this circuit causes the charge in the capacitor to be discharged into the switch or into the latching solenoid, activating it. Depending upon the polarity of the incoming DC power, the discharge of the capacitor will either turn the switch on or off, or will either open or close the solenoid. The release of the contacts also disconnects the secondary switch/solenoid circuit from the power supply lines, thereby eliminating potential lightning strike problems that would otherwise be present with a direct link back to the source.
Any appropriate on/off switch may be employed in the circuit. The controller supplies an appropriate activating or deactivating DC voltage when the switch is to be toggled. Accordingly, most of the time no DC current is carried over the lines, except for the few seconds needed to activate and deactivate the switch at the beginning and end of an operation. This all but eliminates any problems presented by the galvanic effect, and allows for considerably long wire runs.
If a solenoid is used, it should be of the latching variety, which means that once it is activated (opened or closed), it remains that way without the requirement of a constant current running through it, This provides the added benefit of extending the life of the solenoid since the coil thereof is not exposed to constant current which might result in overheating and failure.
It is therefore a primary object of the present invention to provide an improved battery powered switch controller having extended battery life.
It is also a primary object of the present invention to provide a reliable local circuit that may be attached to a far distant DC power supply or controller for use in operating a local switch, or a local latching solenoid attached to a water supply valve.
It is a further important object of the present invention to provide a battery powered programmable irrigation valve controller.
It is another important object of the present invention to provide a battery powered switch controller which does not maintain its activation/deactivation capacitors in a fully charged condition at all times.
It is another important object of the present invention to provide a battery powered controller for operating multiple switches at remote locations.
It is a further important object of the present invention to provide a battery powered programmable controller having circuitry which does not allow each capacitor to be charged until just before it is known to be needed for discharge to activate a switch or solenoid.
It is a further important object of the present invention to provide a battery powered valve controller having a load isolation circuit which engages to separate the high voltage batteries from the capacitors immediately prior to discharge of the capacitors.
It is a further important object of the present invention to provide a battery powered controller having a microprocessor circuit which isolates the capacitor from the high voltage batteries several milliseconds before the solenoid is discharged, so as not to also draw on the capacitor-charging batteries during the discharge operation.
It is a further object of the present invention to provide a battery powered programmable irrigation valve controller in which the circuitry does not perform continuous sampling, but instead samples only at regular intervals.
It is a further object of the present invention to provide a battery powered controller in which the circuitry is not running in a current consuming operation except at regular intervals for a few milliseconds, thereby prolonging the life of the battery.
It is a further object of the present invention to provide a battery powered controller in which the circuit board is encapsulated in epoxy so as to prevent impurities from corroding any of the component parts, and minimizing exposure to electrostatic discharge,
It is a further object of the present invention to provide a battery powered controller which uses lithium batteries for both the high and low voltage batteries because of their greater reliability and long life.
It is a further important object of the present invention to provide a reliable remote DC circuit for use in operating a switch which saves energy by requiring very low current to activate and deactivate the switch.
It is a further important object of the present invention to provide a reliable remote DC circuit for use in operating a latching solenoid attached to a water supply valve requiring a very low current to activate or deactivate the latching solenoid.
It is a further object of the present invention to provide a secondary circuit which includes a capacitor and a switch or latching solenoid that is automatically disconnected from the DC power source when not in use thereby avoiding potential lightning strike problems.
It is a further object of the present invention to provide a reliable circuit for operating a switch or latching solenoid that may be attached to an DC power source over a long run of high gauge (low cost) copper wire without any galvanic effect
It is a further object of the present invention to provide a remote circuit for operating a switch or a latching solenoid attached to a water supply valve that may be battery operated.
It is a further object of the present invention to provide a remote device for operating a remote switch or solenoid that allows for considerable savings in the costs for electric current and the costs associated with great lengths of low (larger) gauge wire.
Other objects of the invention will be apparent from the detailed descriptions and the claims herein.